Radiotherapy is used to treat cancers and other ailments in mammalian (e.g., human and animal) tissue. An exemplary radiotherapy is provided using a linear accelerator (LINAC), whereby a tumor is irradiated by high-energy particles (e.g., electrons, protons, ions and the like). During the course of radiation treatment, images of the tumor and surround tissues may be acquired using an image acquisition device to improve the accuracy of radiation field placement. For example, information revealed by the images may be used to compensate for changes of the tumor due to treatment or due to movement of the patient.
Images may be acquired prior to a treatment session to determine changes of the tumor between sessions, or during a treatment session to determine changes of the tumor due to, for example, movements of the patient. Magnetic Resonance Imaging (MRI) techniques may be used to produce such images thanks to its excellent soft tissue contract and high resolution. However, the acquisition time of MRI images, especially three-dimensional (3D) MRI images, is relatively long. For example, a 3D MRI image may take several minutes to acquire. Such a long acquisition time makes 3D MRI unsuitable for tracking movement related tumor changes during a treatment session.